The present invention pertains to an apparatus and a method for the preparation of a sample bead for use in X-ray fluorescence spectroscopy or other analytical methods such as atomic absorption or inductively coupled plasma.
Several machines are commercially available which provide for the fusion and mixing of a powdered sample together with a flux to provide a solid glass-like sample bead or button for analysis by X-ray fluorescence spectroscopy or other analytical methods Samples to be analyzed include materials such as silicon dioxide, cement, aluminum dioxide, calcium dioxide, magnesium oxide and slag, which are analyzed for the content of their active elements. To provide a sample in a form which can be used in connection with such analysis technique, it must be formed into solid smooth-surfaced shape.
In the prior art systems, high melting temperatures are obtained utilizing a mixture of oxygen and propane which create an oxidizing environment which, at the high temperature, can seriously damage the platinum crucibles holding the sample. Further, with the use of pure oxygen and propane, excessive temperatures can be reached which actually can melt the platinum crucible.
Also, in the prior art systems, the devices poured the mixed molten sample or melt into a casting dish for subsequent cooling into the desired sample shape. However, the dishes typically are positioned adjacent the melting crucible and therefore the temperature of the dishes does not correspond closely to that of the crucible and during the pour step, a sample can cool in an uneven manner thereby crystallizing improperly and possibly cracking rendering the sample unusable.
Furthermore, with gas heating, the crucible was not heated evenly with the bottom becoming hotter than the top. The uneven heating resulting in longer fusion times to melt the flux on the upper edge of the crucible which, in turn, caused the bottom of the crucible to be heated to an unnecessarily high temperature. The heat gradient also tended to cause the flux to stick to the upper portion of the crucible when pouring the molten sample into a casting dish or acid solution.
Finally, in the existent machines used for preparation of X-ray fluorescence samples, it is desired to controllably cool the sample melt once poured into the casting dish. This has been accomplished in the past by utilizing a separate fan or air control delivery system which directs air over the casting dish for cooling. It would be far better if the thermal mass of the environment could be reduced to speed the cooling process.